1. Technical Field
The present invention relates to a liquid container of an air-open type that is suitable for an ink cartridge to be detachably mounted on an ink jet printer. In particular, the present invention relates to a technique that, in a liquid container having a liquid detecting unit for detecting a consumption state of a liquid in a liquid containing portion, can detect a change in acoustic impedance so as to prevent erroneous detection due to sticking of bubbles to the liquid detecting unit.
2. Related Art
As an ink cartridge (liquid container) to be detachably mounted on an ink jet printer, various kinds of air-open type ink cartridges are suggested. The air-open type ink cartridge has, in a container main body that is detachably mounted on a printer, an ink containing portion (liquid containing portion) that contains ink, an ink supply portion (liquid supply portion) that is connected to a printing head (liquid jetting unit) of the printer, an ink guide path (liquid guide path) that guides ink stored in the ink containing portion to the ink supply portion, and an air communicating opening that introduces air from the outside into the ink containing portion according to consumption of the ink in the ink containing portion.
In such an ink cartridge, an ink residual quantity detecting mechanism (liquid detecting unit), in which a sensor having a piezoelectric vibrating body is disposed at a reference height in the liquid containing portion, is provided (for example, see Patent Document 1). In the ink residual quantity detecting mechanism (liquid detecting unit), if the liquid level of ink of the liquid containing portion falls to the reference height due to ink consumption by printing, and fresh air introduced from the air communicating opening into the liquid containing portion according to ink consumption reaches a detection position of the sensor. Then, it is detected, from a change in vibration characteristic (residual vibration) between when the periphery of the sensor is filled with the ink liquid and when air is in contact with the periphery of the sensor, that the liquid level of ink falls to the reference height.
That is, a change of acoustic impedance is detected by causing a piezoelectric device having a piezoelectric element or a vibrating portion of an actuator vibrate, subsequently measuring a counter electromotive force generated by the residual vibration remaining in the vibrating portion, and detecting an amplitude of a resonance frequency or a counter electromotive force waveform. The detection signal is used to display the residual quantity of ink or give notice of a cartridge replacement time.
Patent Document 1: JP-A-2001-146019
However, in the air-open type ink cartridge, air in the liquid containing portion may become bubbles by mixed in the ink due to a vibration at the transportation time after manufactured or fresh air introduced from the air communicating opening into the liquid containing portion according to ink consumption may become minute bubbles due to an impact upon attachment/detachment of the cartridge, and the bubbles may float in the ink liquid. Then, if the bubbles floating in the ink liquid are stuck to the surface of the sensor of the ink residual quantity detecting mechanism, the stuck bubbles may cause a change in residual vibration. Accordingly, presence/absence of ink may be not accurately detected, and it may be erroneously detected that the liquid level of ink falls.
That is, a known air-open type ink cartridge uses a vibration phenomenon, and thus the state of the liquid in the liquid container (including presence/absence of the liquid in the liquid container, the quantity of the liquid, the liquid level of the liquid, the kind of the liquid, the composition of the liquid) can be detected. However, any countermeasure against the erroneous detection due to sticking of the bubbles to the surface of the sensor has not been suggested yet. As a result, the erroneous detection of the ink residual quantity due to sticking of the bubbles to the surface of the sensor may occur.